There is a white eupatorium, Eupatorium rugosum. The most popular garden cultivar is Chocolate, named because of the burgundy leaves.

Since it's a native plant, but also fairly popular in the garden, who knows where the seeds for yours came from.

Is this just blooming now?

I've got a friend who I help with a very wet garden, and across the stream in the woods is a plant which to me looks like a eupatorium, (much likes your photo) but it blooms earlier, in spring, so that always threw me, as I thought most eupatoriums bloom later. Just curious as to whether yours above is in bloom now or whether you were just a bit late in posting this question, lol. Kinda know the answer already but hey...doesn't hurt...

:)
Dee

Thank you for the info, mad_gallica. All the photos of eupatorium I've seen poking around tonight online look just like my plants, so eupatorium it must be. Now I have a name to put with my newcomers. I guess I'll never know where the seeds came from.

Dee, my eupatoriums are blooming right now. I just picked the flower that I photographed a day or two ago. Since I first noticed them several years ago, they have always bloomed in late summer as they are now. They definitely seem to like the wet area alongside my brook where they are growing, like the flowers near your friend's garden. But whether or not all varieties of eupatorium bloom now, I couldn't say. All varieties of plants seem to flower much later here than in southern New England, so I'm uncertain as to whether that could account for the difference in bloom times. (I'm supposed to be zone 4, but sometimes it behaves more like zone 3, because of the higher elevation where my house is, I think.) Not sure if any of this is helpful.

Spedigrees - Eupatorium perfoliatum has leaves that look like the base of the pairs of leaves cup the stem or that it was threaded through the center of the pairs of leaves where they meet. (Technical term for this is perfoliated, hence the species name.) I can't tell from your photo if they do that, but they start blooming a bit earlier than Joe-Pie-Weed, though there is overlap. Like JPW they like wet areas, and they have grown on the floodplain along our stream. The common name is boneset, so I imagine it was used in herbal medicine, I don't know.

The page below has a great photo of the leaves which is the best way to id it. I have no idea why they have labeled it purple boneset, as it's white!

Here is a link that might be useful: Boneset

Thank you for the specific ID, Babs. I went out and took a closer look at my eupatorium plants, parting the weeds and wildflowers to walk out into the swampy area by the brook. There are more plants than I had realized, hidden behind my 'wall of wildflowers' as I call this area, and growing back down to the brook. My plants definitely have the same leaf structure as the photo in the link you posted, so it must be eupatorium perfoliatum.

The Joe Pyeweed (which I didn't know I had until Jane identified it for me - I'd misIDed it as swamp milkweed) does bloom first, but now both are blooming in the overlap you mentioned.

I found an article that said eupatorium perfoliatum was used in herbal medicine to promote healing of broken bones, hence the name. There seem to be a variety of common names for the different varieties of eupatorium, but now that I know which variety mine is, I have a common name to put with it.